Process for dedusting comminuted soap



Sept. 7, 1943. B. MAXWELL lar AL inocEss FOR DEDUSTING oMMINuTED sQAPFiled Ag. 15, 1940 Il 'By L'lrarles Z'Hhwad INVEN'roR S award L'. han#Patented Sept. 7, 1943 PROCESS FOR DEDSUSTING COMIMJINUTED Bernard L.Maxwell, Reading, and Charles T. Atwood. Belmont, Mass., assignors toLever Brothers Company, Cambridge, Mass., a corporation of MaineApplication August 15, 1940, SerialI No. 352,738

3 Claims.

This invention relates to classiication of finely comminuted materials,and has particular reference to an improved method for separatingexcessively fine soap particles from comminuted soaps, and the improvedsoap product.

In general, the forming of comminuted soaps is accomplished by spraydrying the liquid soap stock to obtain particles in characteristicgranule form. The dried soap particles are classified Within designatedlimits of particle size by a screening opera-tion, and packaged.Commercial grades of comminuted soap ordinarily range in particle sizebetween those 'particles passing a 20 mesh screen and retained by an 80mesh screen, the oversized particles and fines being returned to themanufacturing system for reprocessing. However, with screening methodspresently in use, soap fines and dust occur in the packaged product inamounts varying between 5% and 30% of the total pack.

The presence of soap iines and dust in the comminuted product isobjectionable for several reasons. The ne particles have an irritatingeiect on the nasal passages. Such a dust irritating eiect may becomeapparent in several ways. For example, the user of a comminuted soap ofundesirably high dust content may sneeze and cough on opening a packageof such soap or in pouring it out for use. is also particularly apparentin the comminuted soap manufacturing process. Objectionably largeamounts of dust are formed during the manufac- This undesirable effectture of comminuted soap and the problem is dificult to overcome in viewof the pulverulent properties of the soap particles.

Soap dust extracting methods heretofore employed in comminuted soapmanufacture have been, in most cases, entirely inadequate, land in manycases the use of dust masks by workmen associated with the screening andpackaging rooms is necessary.

Moreover, the wastage of soap between the spray drying and screeningoperations by excessive sifting or filtration from apparatus andentrainment of fine particles in the air, is considerable. amounts offines in bulk comminuted soaps causes undesirable variancein'bulk-weight proportions of the packaged granules. I

The forming of small amounts of nes in comminuted soaps during screeningand packaging is unavoidable, due to agitation of the particles inherentin these operations. However, the accumulation of large amounts of finesin bulk comminuted soaps during manufacture and prior to It has beenfound that the presence of large screening leads directly to airpollution through excessive dusting, and enhances the ineillciency ofthe screening operation as an accurate method of lparticleclassification, due to clogging of the screen mesh.

It has been discovered that a comminuted soap containing in the bulkonly those particles 'retained by a mesh screen is not objectionablefrom the point of view of causing the nasal irritation often indicatedby excessive coughing or sneezing. Removal and collection of soap dustAof such neness is not satisfactorily accomplished during the screeningoperation due to the tendency of the bulk soap to retain a portion ofthe dust, and the tendency of microscopic particles to entrain in airupon agitation, the eiect of gravity thereon being negligible.Similarly, apparatus presently available for classication and dedustingof relatively hard materials such as case hardened soap drops and thelike, are not adaptable to the relining of bulk comminuted soaps, due tothe fragile nature of the soap particle and the tendency to crumble withexcessive agitation, reducing the percentage of packageable dedustedproduct. 1

It is an object of the present invention to provide an improved methodof separating excessively fine soap particles from bulk comminutedsoaps, without undue loss of packageable soap by powdering, underexcessive agitation.

A further object is to provide a method of controlling dust accumulationand ltration in comminuted soaps to produce a comminuted product havinga very lowfdust content.

A still further object is to provide a bulk comminuted soap producthaving a low content, preferable less than 1%, of objectionable finesand soap dust, upon packaging.

Other objects and advantages will appear from the following descriptionand drawing, wherein:

Figure 1 is a view in verticalsection of the soap particles classifyingand dedusting apparatus of the invention; y

Figure 2 is a similar view of a modiiied form apparatus of the presentinvention; and

Figure 3 is a}view in top section along the line 3-3 of Figure 2 andlooking in the direction of the arrows. l l

Referring to Figure 1 of the drawing, the numera1 lll indicates a towerpreferably rectangular in cross-section, having a top wall I I andbottom plates l2 converging to a particle discharge outlet i3. A hopperI4 discharges into a tortuous chamber I5 enclosed by a series of rampsI6 positioned to form inclined falls throughout the soap particles intocontainers.

tower. The chamber I5 at its lower portion connects with the outlet I3,which discharges to a conveyor 24 or other device suitable to divert theA suction pump I1 adapted to draw a ilo'w of gaseous medium such as airthrough an air inlet I8 into the chamber I5 at its lowerportion exhaustsspent gaseous mediultimate exhaustion through the hood I9 is avoided. Byproper adjustment of the dampers um through an aperture in the upperwall II by means of a hood I9 and a conduit 20. A damper 2i at the upperportion of the chamber I5 proiary conduits 22 opening into the chamberI5 at points adjacent the sequences of the ramps I6. The conduits 22permit the carrier air to be drawn oil.' at intermediate zones in thetower. Dampers 23 in each of the conduits 22 permit of controlof therate of exhaustion of gaseous medium through each. There is also acontrol damper 23 in the draw-off conduit 20. Y

In operation, the pump I1 is operated to provide an airilow in chamberI5. This airflow has preferably a iixed velocity determined inaccordance with the degree of particle separatory action desired. Thecomminuted soap product is continuously introduced into the chamber I5through the hopper'll, falling by gravity over the inclined .ramps I6 toultimate discharge through the outlet I3. The slope of the ramps I6 isselected to permit of free gravitational fall of the particles ofsoapwhich are subjected to a series of winnowing actions as they pass overthe ends of the ramp sequences and fall by gravity through the upowingair to the surface of the ramp next below. It is essential that the rateof feed and the slope of the ramps I8 be correlated to obtain a particleflow characterized by minimum agitation, in order to preserve theparticle form of the packable soap and avoid pulverization. The air,traveling counter to the particle fall, entrains and carries theexcessively iine particles of soap dust through the hood I9 and conduit20 to suitable particle recovery means, not shown, such as a cycloneseparator, or a dust bag for example. 'I'he degree of particleseparation eiiected will depend upon the velocity of the flow of air inthe tortuous chamber I5, which velocity may be varied as desired byproper manipulation of the damper 2l. For example, if it is desired toseparate only those dust particles passing through a 140 mesh screenfrom the bulk soap, a moderate counter-ilow velocity may be Provided byopening the damper 2|. If it is desired to effect removal of all soapilnes and dust passing through, for instance, an

80 mesh screen, the velocity 0f the counterilow may be duly increased byclosing the damper 2| to exert the full effect of the suction generatedby the pump I1 on the counterflow in the chamber I5.

In the modication shown in Figure 2 of the drawing, comminuted soap isintroduced into the chamber I5 and a suitable gaseous counterflowugenerated therein, as described. By means of the 23 and 23', the rate ofwithdrawal of portions of the airilow in the chamber I5'may becontrolled inaccordance with previously determined condi'- tions of dustconcentration in the soap bulk, and the airflow velocity desired atdesignated points along the' length of the chamber I5.- If desired,additional air may be bled into the chamber at points intermediate theends thereof to replace the dust-laden air withdrawn through conduits22, thus avoiding operating at ldecreasing linear velocities from thebottom to the top ofthe chamber. For instance, as the maximumconcentration of dust in the comminuted soap bulk will occur luponinitial introduction of the soap par--` ticles into the chamber I5, itmay be desirable to introduce additional air and, to operate the topauxiliary conduit 22 with the damper 23 in position to restrict the ilowtherein and thus main-A tain a maximum velocity'of the counterilow atthe nrst ramp sequence. The number of auxiliary conduits 22 may bevaried ,as desired.

The angle of incline of the ramps I5 may be determined in accordancewith the relationship of the ramp slope to the desired rate of travel ofthe particles thereover. The rate .of travel is also dependent upon thesize and density of the soap particles and the velocity of the upwardiiow of ai/r. By reducing the area. between the ramps at points alongthe lengthy of the tower III, the velocity of the airflow will be`proportionately increased at those points. It has been noted, forexample, ina test unit having a capacity of 200 ounces per minute ofastandard spray dried soap screen through 20 mh and with 6 ramps orfalls at an angle of 45 degreesthat a spacing of eleven inches wasdesirable between the inclined ramps. 'I'he air volume was about 450cubic feet per minute and the velocity of iiow about 500 feet perminute. A screen analysis of the soap originally and after treatmentgives the following data:

By simple experimentation with ramp positioning, airiiow velocity andvolume and positioning of the damper 2|, in accordance with theprinciples indicated and taking the aforementioned factors of particlesize, density and rate of feed into consideration, operation 'of thenovel particle separating and dedusting apparatus of the invention maybe maintained at peak emciency to obtain a dedusted bulk comminuted soapproduct having a percentage content of objection-able iines and soapdust considerably under 1.0% of the total bulk. For a given rate of feedof soap particles, which rate has an optimum value for any given size ofthe apparatus there will be a critical volume of airflow determined bythe setting of the damper 2I, and a critical velocity of airflow,determined by the spacing between the ramps I6 and the setting of damper2i, at which adjustment a maximum eiliciency of dust separation bothfrom the mass of soap particles as they pass from the surface of theramps and from the particle screen as the' particles. pass across theupflowing air. This, furthermore, as a result of our` invention, may beamplified Without undue loss of packable soap.

granules as a result of the separation. l Desirable results, we havefound, may be obtained commercially by utilizing an air volume of about6000 cubic feet per minute and an air velocity of about 600 feet perminute. When operating under these conditions ofI air velocityandvolume, the width of the unit preferably is aboutl feet and the spacingbetween the inclined ramps preferably is about twelve inches. Obviously,for commercial purposes, a greater capacity may be obtained by utilizingmultiple towers. `For example, a battery of three towers operating underthe above conditions of air volume and velocity will have a capacity ofabout 40,000 lbs. of soap per hour. With this rate of feed, a materialcontaining 3 to 4% of nes through 140 mesh is reduced in lines contentto less than 1%. l

While it is preferred to carry out the method of the invention in acomminuted soap manufacturing system prior to screening or otherwiseclassifying the soap vparticles for packaging, in order to expediteclassification, the dedusting operation may be carried out with equallysuccessful results subsequent to screening, or at any other point in themanufacturing process subsequent to spray drying of the soap particles.'

By incorporating rthe method of the present invention into presentlyused processes for manu-- facturing comminuted soap,operatinginelciencies incurred through air pollution and waste ofproduct through dust ltration are eliminated. The method of theinvention provides a bulk comminuted soap product with an effectivelystandardized bulk-weight proportion, and having a soap dust content ofless than 1% prior to packaging.

While the invention has been described herein with reference to specificstructure, these references are made by way of illustration. It isintended to include all equivalents within the scope of the invention,which is to be limited only as dened in the appended claims.

We claim:

1. A method of dedustlng bulk comminuted soaps comprising particles ofvarying sizes and including substantially in excess of 1% of particlespassing through a mesh sieve, comprising conducting the bulk soap in acontinuously ilowing thinly dispersed particle layer over a tortuouspath with minimum distintegration of the particles, providing successiveintervals of free gravitational fall of the said particle layer at eachsuccessive change in direction of the tortuous path to form successivecurtains of falling particles, passing a gaseous carrier medium countertothe iiow of the curtains of falling particles and at an angle thereto,and at a velocity to provide a series of successive winnowing actions onthe soap particles at each of said successive changes in direction ofthe tortuous path to entrain the soap dust content of the particle layerto an extent that the particles so treated will have less than 1%passing through a 140 mesh sieve, and separating the gaseous carriermedium with the entrained dust from the soap particles.

v2. A method of treating 'a pre-formed comminuted soap product havingparticles of varying sizes and containing substantially in excess of 1%of ine particles passing through a 140 mesh sieve, which comprisesforming a plurality` of vertically falling curtains of said particles,passing a gaseous mediumV through said curtains of particles at an angleto the vertically falling particles and at a velocity such as to entraina major portion of the fine particles in the gaseous medium so that theparticles falling through said gaseous medium will contain less than 1%of particles passing through a 140 mesh sieve.

3. A method of treating a pre-formed comminuted soap product havingparticles of various sizes and including substantially in excess of 1%of particles passing a 140 mesh Sieve, which BERNARD L. MAXWEIL. CHARLEST. ATWOOD.

